Filter device, in particular for high-pressure applications in a molten polymer filtration

ABSTRACT

The invention relates to a filter device, in particular for high-pressure applications in a molten polymer filtration, with a screw-in piece ( 10 ), provided with a first threaded section ( 12 ), for fixing the filter device, a second threaded section ( 14 ), for fixing a filter medium ( 16 ), in particular in the form of a metal wool and with a perforated support tube ( 18 ) for the metal wool. The other free end thereof is provided with a volume displacer ( 24 ), whereby the metal wool is surrounded by a support grid ( 20 ) and fixed by two fixing pieces ( 28, 30 ), held at a separation from each other by means of the support grid ( 20 ), one of which ( 28 ) serves for the fixing to the second threaded section ( 14 ) of the screw-in piece ( 10 ) and the other as a handle ( 30 ) for the fixing thus carried out. As a result of the volume displacer  924 ) being a one-piece component of the support tube ( 18 ) and the fixing piece ( 30 ) in the form of a handle covering the volume displacer ( 24 ), the filter device is significantly improved in that the above permits a simple and rapid assembly procedure for the exchangeable filter medium and also the filter element construction is held such as to be free of damaging torsional loads.

[0001] The invention relates to a filter device, in particular forhigh-pressure applications in a molten polymer filtration, having ascrew-in component which is provided with a first threaded section forfixing the filter device, which has a second threaded section, inparticular in the form of metal wool for fixing a filter medium, andwhich has for the metal wool a perforated supporting tube the other,free, end of which is provided with a volume displacement component, themetal wool being enclosed in a support grid and retained by two fixingcomponents, which, spaced a certain distance from each other by thesupport grid, serve the purpose of fixing on the second threaded sectionof the screw-in component and also represent a handle for the fixinginvolved.

[0002] WO 90/00434 discloses provision, between the first and secondthreaded section of the screw-in component, of an annular flange onwhich an annular seal may be supported, a seal which may be brought intocontact by its other annular surface with the screw-on fixing componentof the filter medium. The fixing component in question is provided onits outer circumference with setscrews positioned diametrically oppositeeach other the purpose of which it is to facilitate the screw-onprocess. On the opposite side of the filter medium the latter is alsofixed to another fixing component, the latter also having on its outercircumference screw-in openings positioned diametrically opposite eachother, which serve the purpose of application of a fixing tool, so thatit is possible to use the fixing tool and the auxiliary fixing means inthe form of the setscrews to carry out a screw-on application processpotentially free of torsion, in order in this way to keep the filtermedium, in particular one in the form of metal wool, free of torsionalstresses for later polymer melt filtration and in order not to damagethe support grid which encloses the metal wool filter medium to shieldit from the exterior. The volume displacement component is then screwedonto this fixing component in the direction of the supporting tube.While this disclosed solution does make it possible to replace a fouledfilter medium with a new filter element having fixing components and toleave the valuable stainless steel components in the form of thescrew-in component and the supporting tube at the place of assembly, theassembly process itself is difficult to carry out because ofinsufficient rigidity of the filter element structure which complicatesthe replacement process. The possibility is also not to be excluded ofbuildup of torsional stresses in the support grid and in the filtermedium in the fixing processes, so that failure is possible especiallyin a high-pressure application.

[0003] DE 43 43 270 A1 discloses a spinning head for spinning polymermelts, with an upper element and a nozzle block housing with a nozzleplate having a maximum area of 90 cm² and a melt channel with filtercartridge. In that in the solution as disclosed a single filtercartridge is mounted upstream in the direction of flow from each nozzleplate, in that the filter cartridge consists of a seamless wire clothcylinder through which flow proceeds radially from the exterior towardthe interior, the cylinder having a cap at the upper end and aconnecting piece tapering downward through which melt is conducted atthe lower end, in that the zone of the melt channel receiving the filtercartridge is configured as a cone, at least in the lower third, and inthat the tapering connecting piece of the filter cartridge is pressedinto the cone by the polymer melt so as to be self-sealing, uniform flowof the polymer melt with dead spaces eliminated is achieved to thegreatest extent possible. A volume displacement component which is aone-piece component of a supporting tube for the filter medium isprovided at the upper end of the filter cartridge, opposite the lowerend of the cone referred to. Despite the resulting reinforcement of thesystem as a whole, susceptibility to torsional stresses is still presentand on the whole the process of filter element replacement isaccomplished only with difficulty, virtually complete disassembly of thedisclosed spinning head being required for the purpose.

[0004] WO 01/52966 A1 discloses a filter device with a filter housinghaving a filter admission and filter discharge, as well as a filterelement which divides a filter chamber into two component chambers. Inthat in this solution one component chamber narrows in cross-sectionfrom the filter admission toward the filter discharge, conicalconfiguration of at least one of the two component chambers separated bythe filter element is provided. This permits achievement of optimaldwell time distribution inside the filter device, along with a uniformrate of flow, a characteristic which performs an essential functionespecially in the case of high-viscosity fluids such as polymer melts.In the disclosed solution in question a fixing component configured as ahandle encircles the volume displacement component in the interior. Butsince the filter medium surrounding the supporting tube rests on thefixing component in question and at the opposite end in receptaclecomponents rigidly connected to the housing, the harmful torsionalstresses already described also arise in a process of disassembly andreplacement of the filter element. Replacement of the filter elementsalso entails high cost.

[0005] On the basis of this state of the art the object of the inventionis further improvement in the disclosed filter device so as to permitsimple and rapid assembly of the filter medium to be replaced, as wellas keeping the filter element design free of harmful stresses,especially ones in the form of torsional stresses. The object as thusformulated is attained with a filter device having the featuresspecified in claim 1.

[0006] As a result of the characteristics specified in claim 1 in itsentirety, the volume displacement component is an integral component ofthe supporting tube and the fixing component configured as a handleencircles the volume displacement component. Consequently, the volumedisplacement component as a component of the supporting tube no longerdiminishes the operating cross-section for the fixing componentconfigured as handle so that this fixing component is reinforced as asealing or cover component to the extent that a rigid structure isachieved for the filter element as a whole as replacement modular unitso that torsional forces harmful to the filter medium in the fixing orscrew-on process may be largely prevented. A screw-in cartridge ofstable configuration is rather obtained and the costly volumedisplacement component may remain in the supporting tube in areplacement process and need not be removed in a detailed process. Thesolution claimed for the invention also makes it possible to carry outthe fixing and exchange process exclusively by way of the handle, sothat additional auxiliary assembly components such as setscrews or thelike may be entirely dispensed with on the other fixing component withthe threaded section.

[0007] In one preferred embodiment of the filter device claimed for theinvention provision is also made such that, when the screw-in componenthas been introduced, an annular seal, in particular one in the form of ametal wool seal, is mounted between the first and the second threadedsection of the fixing component. A separate annular seal on an annularflange of the screw-in component, such as that provided in the disclosedsolution, may be completely dispensed with and yet reliable sealing isthereby achieved.

[0008] In another, especially preferred, embodiment of the filter deviceclaimed for the invention the filter medium is retained by projectionsof material, especially also by indentations of the fixing components,at specified fixing points. The fixing points preferably represent anintegral component of the fixing components. The respectiveconfiguration provides for a torsion-free fixing and replacement processfor the filter medium, so that this medium is kept largely free ofharmful material stresses.

[0009] In another preferred embodiment of the filter device claimed forthe invention the fixing component serving as handle has the filterdevice spaced a certain distance axially from the volume displacementcomponent, this volume displacement component being provided withsloping support surfaces which are at least to some extent in contactwith supporting surfaces of the handle when a fixing component has beenscrewed in. The respective configuration, with the volume displacementcomponent resting on the handle, provides security of contact makingcertain that the threading of the fixing component to be screwed on willnot be screwed on too tightly, a condition which could damage thethreading. Contact is also established such that the metal wool asfilter medium, together with its support grid, is not subjected toharmful torsional forces.

[0010] Other advantageous embodiments are specified in the dependentclaims.

[0011] The filter device claimed for the invention is described ingreater detail on the basis of two embodiments with reference to thedrawing, in which, in the form of diagrams not drawn to scale,

[0012]FIG. 1 presents a first embodiment of the filter device, partly asa side view and partly in cross-section;

[0013]FIG. 2 a section along line I-I in FIG. 1; and

[0014]FIG. 3 a longitudinal view of the second embodiment, also incross-section and as a side view.

[0015] The filter device claimed for the invention in the embodimentshown in FIGS. 1 and 2 will be explained first. The second embodimentwill then be presented, but only to the extent that it differsessentially from the first embodiment.

[0016] The filter device as specified for the exemplary embodiments isprovided in particular for high-pressure use in polymer melt filtration.The filter device has a screw-in component 10 which is provided forfixing the filter device in an overall filter module (not shown) havinga first threaded section 12. The screw-in component 10 also has asecond, downstream, threaded section 14 for fixing a filter medium 16,in this instance a metal wool suitable for polymer melt filtration. Inthe interior the filter medium 16 rests on a perforated supporting tube18 and on the outside the metal wool or filter medium 16 is enclosed ina support grid 20 with rectangular passage areas 22. The supporting tube18 itself is rigidly connected on one of its ends to screw-in component10, especially by way of a welded connection, and on its other free endto a volume displacement component 24 also connected to it in particularby way of a welded seam. The volume displacement component 24 is engagedby its tapering fluid conducting component in the supporting tube 18 andthus serves to even out the polymer melt flow inside the supporting tubein the direction of the discharge opening 26 inside the screw-incomponent 10.

[0017] Both the support grid 20 and the filter medium 16 are retained ontwo fixing components 28, 30 which are kept at the specified distancebetween them, in particular by way of the filter medium 16. The firstfixing component 28 serves to secure the filter medium 16 on the secondthreaded section 14 of the screw-in component 10, while the secondfixing component 30 is provided as a handle for the fixing processinvolved. The overall structure of fixing components 28, 30 with supportgrid 20 and filter medium 16 is accordingly configured so that a processof screwing in and unscrewing of the respective filter unit is madepossible essentially by engagement of the handle in the form of thesecond fixing component 30. The direction provided for passage of thepolymer melt, especially at high pressure values, extends from theexterior toward the interior, initially by way of the support grid 20,then by way of the filter medium 16 and perforations in the supportingtube 18 to the interior of the filter device, the polymer melt thenleaving the filter device by way of the discharge opening 26 forsubsequent use after impurities have been removed from it in thismanner. If the metal wool is added as filter medium 16 removingimpurities, the possibility accordingly exists of making a new filtermedium available for repeated use by way of the handle 30, by detachingthe screw-in component 10 by way of the first fixing component 28. Sincethe second fixing component 30 more or less encloses the volumedisplacement component 24, the handle in question may be designed to behighly rigid, a condition favoring the overall rigidity for thereplacement components, so that harmful torsional stresses, especiallythose arising in the fixing process, may be kept away from the filtermedium with its support grid 20.

[0018] There is mounted between the first threaded section 12 and thesecond threaded section 14 of the screw-in component 10 an annular seal32 on the free frontal surface of the first fixing component 28 afterthis component has been introduced, in particular a seal in the form ofa metal wool seal. This presents the advantage that the filter element,which has only one seal, is kept replaceable and yet reliable sealing ofthe interior of the filter device from the surroundings is provided inthis way during later use. Unintended escape of the polymer melt isaccordingly reliably prevented, even in decidedly high-pressureapplications.

[0019] The filter medium 16 is retained in specific fixing positions 28,30 in recesses in the fixing components by projections of material, inparticular in the embodiment shown in FIG. 1. The inherently flexiblemetal wool as filter medium 16 may thus be fixed to the projections ofmaterial 34 by pressing processes; the fixing technique involved may becost effectively applied and yet permits reliable fixing. The fixingpositions referred to are themselves integral components of the fixingcomponents 28, 30 and the respective fixing position continues as anextension in the fixing component 28, 30. The latter also promotes theoverall reinforcement of the system. As is to be seen in FIG. 2 inparticular, the filter medium 16 extends in pleated form around thesupporting tube 18 and is enclosed toward the exterior by the supportgrid 20.

[0020] The second fixing component 30 serving as handle is spaced acertain distance 36 in the axial direction of the filter device from thevolume displacement component 24, the volume displacement component 24being provided with tapering support areas 38 which are at least to someextent in contact with support surfaces 40 of the second fixingcomponent after the first fixing component has been introduced. Asupporting force may thus be exerted on the volume displacementcomponent 24 during the screw-in process; the volume displacementcomponent 24 may then also serve as backing in order to preventexcessive tightening on the threaded sections in the area of the firstfixing component 28. In addition, forces arising during filtration maythen be reliably diverted by way of the support areas 38, 40 referred tointo the base structure of the supporting tube 18 with screw-incomponent 10. The latter also contributes to reinforcement of the systemas a whole, so as to provide the possibility of shielding the filtermedium 16 itself from the effects of harmful forces.

[0021] The second embodiment will now be described in detail withreference to FIG. 3. The same reference numbers are employed as thoseused for the first embodiment, and the present embodiment willaccordingly be explained only to the extent that it differs from thefirst embodiment illustrated in FIGS. 1 and 2.

[0022] First of all, in the second embodiment shown in FIG. 3 the fixingcomponent 30 serving as handle is provided with a tapered element 42extending outward toward the exterior. In addition to fixing of thefilter device by way of the screw-in component 10, the tapered element42 in question also provides the option of fixing inside an overallfilter device (not shown), in addition to that of fixing the filterdevice by way of the screw-in component 10. In addition, each of thefirst and second fixing component 28, 30 consists of two sections 28a,b, 30 a,b, each of the respective sections being rigidly connected toeach other by a weld seam. The respective section 28 b, 30 b has acorbel projecting inward, and the filter medium 16 is thickened by abuilt-up weld seam so that the weld seam overlaps the section so thatthe filter medium 16 may be fixed on the sections 28 b, 30 b. This makesit possible to obtain a very slim overall filter device in which thesupport grid 20 more or less determines the outer diameter of theoverall filter device.

[0023] Both embodiments have in common the feature that the screw-incomponent 10 forms with the supporting tube 18 and the volumedisplacement component 24 a module present on an overall filter unit andthat the filter medium 16 with its two fixing components 28, 30, whichis subject to wear, is separable as replacement module from the fixedmodule. If the filter device is used for filtration of polymer melts,all essential structural components are made of stainless steelmaterials.

1. A filter device, in particular for high-pressure applications in amolten polymer filtration, having a screw-in component (10) which isprovided with a first threaded section (12) for fixing the filterdevice, which has a second threaded section (14) for fixing a filtermedium (16), especially one in the form of metal wool, and which has forthe metal wool a perforated supporting tube (18) provided on its otherfree end with a volume displacement component (24), the metal woolenclosed in a support grid (20) being retained by two fixing components(28, 30) which, being spaced a certain distance from each other by thesupport grid (20), one of which (28) serves the purpose of fixing on asecond threaded section (14) of the screw-in component (10) and otherrepresent a handle (30) for the respective fixing, the volumedisplacement component (24) being an integral component of thesupporting tube (18), and the fixing component (30) being in the form ofa handle encircling the volume displacement component (24).
 2. Thefilter device as claimed in claim 1, wherein an annular seal (32), inparticular one in the form of a metal wool seal, is mounted between thefirst (12) and the second (14) threaded sections of the screw-incomponent (10) when the first fixing component (28) has been screwed on,on the free frontal surface of such first fixing component (28).
 3. Thefilter device as claimed in claim 1, wherein the filter medium (16) isretained by projections of material (34), in particular also by recessesin the fixing components (28, 30), in specific fixing positions on thesefixing components (28, 30).
 4. The filter device as claimed in claim 3,wherein the fixing positions are an integral component of the fixingcomponents (28, 30).
 5. The filter device as claimed in claims 1,wherein the fixing component (30) serving as handle is spaced a certaindistance (36) in the axial direction of the filter device from thevolume displacement component (24) and wherein the volume displacementcomponent (24) is provided with tapering support areas (38) which are atleast to some extent in contact with the support area (40) of the handle(30) after one of the fixing components (28) has been screwed in.
 6. Thefilter device as claimed in claims 1, wherein the fixing component (30)serving as handle is provided with a tapered element (42).
 7. The filterdevice as claimed in claims 3, wherein one fixing component (28), whichserves the purpose of fixing on the second threaded section (14),consists of two sections (28 a,b) interconnected in particular by a weldseam one section of which (28 a) has the threaded component for thesecond threaded section (14) of the screw-in component (10) and theother section (28 b) of which has the projection of material for fixingthe filter medium (16).
 8. The filter device as claimed in claims 1,wherein the screw-in component (10) forms with the supporting tube (18)and the volume displacement component (24) a lasting structural unit,and wherein the filter medium (16) with its fixing components (28, 30)forms a replacement unit subject to wear.
 9. The filter device asclaimed in claim 9, wherein both modular units consist more or less ofstainless steel materials.